In the field of vibration damping rubber components for vehicles, vibration damping rubber bushings having a design that includes rigid, round outer and inner cylinders and a rubber elastic body integrally vulcanization bonded to the outer and inner cylinders to provide elastic linkage thereof enjoy widespread use as automotive trailing arm bushings, torque rod bushings, and the like.
Such a vibration damping rubber bushing is typically assembled to a cylindrical mated component made of metal and having a circular inside peripheral face, to construct a bushing assembly in which the outside peripheral face of the outer cylinder is press fit in the axial direction into the cylindrical mated component.
In the prior art, the outer cylinder of the vibration damping rubber bushing is made of metal, and when the vibration damping rubber bushing is press fit into the mated component with a prescribed level of lap dimension at the outside peripheral face of the metal outer cylinder, the resultant strong friction produced between the outside peripheral face of the outer cylinder and the inside peripheral face of the mated component serves to prevent the vibration damping rubber bushing from becoming dislodged from or rotating within the mated component.
More recently, with the aim of reducing weight, the use of resin for the outer cylinder of vibration damping rubber bushings has been contemplated. In such cases however, if the outer cylinder of the vibration damping rubber bushing is simply assembled to the mated component by press fitting, that is, if the vibration damping rubber bushing is secured to the mated component merely through frictional force acting between the outside peripheral face of the resin outer cylinder and the inside peripheral face of the mated component, even if the press fit initially has the prescribed level of lap dimension, the fastening force, i.e. the level of force that will dislodge the vibration damping rubber bushing from the mated component, will be low, thus posing the risk that if subjected to an outside force, the vibration damping rubber bushing may become mispositioned with respect to the mated component, or in some instances dislodged entirely.
To date, various different strategies for addressing this issue in vibration damping rubber bushings that employ a resin outer cylinder have been studied and proposed. One example is depicted in FIG. 10 (disclosed in Patent Citation 1 below). In the drawing, 200 denotes a vibration damping rubber bushing composed of a round outer cylinder 202 made of resin, an inner cylinder 204 made of metal, and a rubber elastic body 206 integrally vulcanization bonded to the outer cylinder 202 and the inner cylinder 204 providing elastic linkage between them.
208 denotes a mated component of cylindrical shape made of metal and having a circular inside peripheral face. The vibration damping rubber bushing 200 is press fit in the axial direction into the mated component 208 so that the outside peripheral face of the outer cylinder 202 is held fitting therein. The resin outer cylinder 202 has a flange portion 210 of annular form at one axial end (the bottom end in the drawing), and through abutment of this flange portion 210 against the axial end face of the mated component 208, the vibration damping rubber bushing 200 is prevented from becoming dislodged in the upward direction in FIG. 10.
The outer cylinder 202 in the section thereof that is situated at its other axial end to the opposite side and that protrudes out in the axial direction from the mated component 208 has partially thick-walled interlocking portion (detent portion) 218 provided with sloping faces 214, 216 that slope in mutually opposite directions. Once the vibration damping rubber bushing 200 is press fit into the mated component 208, this interlocking portion 218 interlocks with the axial end face of the mated component 210, and specifically interlocks with the axial end face on the opposite side from the flange portion 210, thereby preventing the vibration damping rubber bushing 200 from becoming dislodged from the mated component 208 in the downward direction in FIG. 10.
However, while the design depicted in FIG. 10 affords some improvement in terms of fastening force of the vibration damping rubber bushing 200 to the mated component 208 as compared with a vibration damping rubber bushing 200 devoid of special measures for this purpose, the extent of the improvement is minimal, so the level of force needed to dislodge the vibration damping rubber bushing 200 from the mated component 208 is not sufficiently high, and there is a risk that the vibration damping rubber bushing 200 may experience rotation relative to the mated component 208 in the rotational direction as well.
If the vibration damping rubber bushing 200 becomes mispositioned in the axial direction or experiences mispositioning in the rotational direction with respect to the mated component 208, the vibration damping rubber bushing 200 may fail to produce the intended intrinsic vibration damping function, and in some instances there is a risk of the vibration damping rubber bushing 200 becoming dislodged from the mated component 208 when subjected to outside force.
Another known approach disclosed in the prior art is a method which involves subjecting the inside peripheral face of the mated component to blasting treatment so as to increase surface roughness thereof. This is for the purpose of increasing the fastening force of the vibration damping rubber bushing to the mated component, and primarily the level of force needed to dislodge it.
For example, in paragraph [0038] of Patent Citation 2 below, it is disclosed to carry out blasting treatment of the inside peripheral face of the mated component of Comparative Example 2 of FIG. 7.
However, even such methods that involve imparting irregularities to the inside peripheral face of the mated component through blasting treatment do not afford sufficient improvement in the level of force needed to dislodge the vibration damping rubber bushing.